AbstractWe have previously reported that EBNA-5, one of the Epstein-Barr
virus-encoded proteins, accumulates in the nuclear bodies
containing PML, the promyelocytic leukemia associated protein. In
this study, we examine the intranuclear distribution of SV40
large T-antigen (SV40T), the p53 tumor suppressor protein (p53),
and PML in a conditionally immortalized cell line, IDH4. In IDH4
cells, the expression of SV40T is regulated by a dexamethasone
(Dex)-driven promoter. Withdrawal of Dex results in
down-regulation of SV40T and growth arrest, whereas addition of
Dex to the growth-arrested cells results in up-regulation of
SV40T and proliferation. In proliferating IDH4 cells, SV40T is
concentrated in nuclear dots that are also positive for p53. Many
of these dots are juxtaposed to PML positive structures but do
not colocalize with them. After removal of Dex, SV40T-p53 dots
gradually disappear, while the PML structures remain. Induction
of SV40T in nonproliferating IDH4 cells causes a coordinated
redistribution of SV40T and p53. The immunostaining for SV40T and
p53 is first weak, then strong with a homogeneous distribution,
and 3-4 days later becomes dot-like again. This reappearance of
SV40T-p53 dots coincides with the recovery of proliferation in
restimulated IDH4 cells. Also, the p53 pattern correlates with
the SV40T pattern with regard to both morphology and intensity
during both suppression and induction of SV40T. Taken together,
our data suggest that (i) the level of p53 is coregulated with
the level of SV40T in a dose-dependent fashion; (ii) the
formation of SV40T-p53 nuclear dots correlates with the
transformed phenotype; (iii) the SV40T-p53 dots localize
preferentially to the neighborhood of PML bodies which are
already present in normal cells.